Electro-Magnetic Interference (EMI) shielding is required on certain semiconductor devices in order to minimize EMI radiation from the semiconductor device. EMI shielding is further required to prevent EMI radiation from external sources from interfering with operation of the semiconductor device.
EMI shielding is generally accomplished in one of three ways. A first method is to attach a metal can over the component after the component is attached to the motherboard. However, shield attach on the mother board has several problems. First, shield attach can be costly and a low yielding process. External shields soldered to the motherboard further require additional board space.
An alternative to the shield attached method described above is an embedded EMI shield. In an embedded shield, the metal EMI shield is directly attached to the semiconductor package substrate by means of solder or a conductive adhesive. The shield may be fully embedded within the mold compound of the finished package or can be exposed after assembly. In either case, the addition of a metal shield as a component attached to the top surface of the substrate is problematic for several reasons. First, the addition of a metal shield as a component attached to the top surface of the substrate requires a significant amount of additional space on the package substrate. Second, it can be difficult to transfer mold in and around the metal shield to fully encapsulate the semiconductor package. Shield attach is also problematic due to flux creep after the shield is attached and delamination and extrusion issues if solder is used to attach the shield. Metal shields also increase the thickness of the component and may inhibit the ability to inspect components under the shield during the assembly process.
The third method is the conventional conformal shield. In this method, all of the components are placed on the substrate and the substrate, or strip, is over-molded using unit molding, or pin gate molding where individual mold caps are defined within the strip such that upward facing, exposed pads in the substrate remain exposed after the mold operation. A conductive coating is then applied to the strip such that it covers the units and also makes electrical contact to the upward facing pads. The strip is then singulated into individual units. While this technique eliminates the molding process concerns associated with the aforementioned embedded shield method, it does not eliminate the added substrate size required to form the so-called upward facing, exposed pads. Therefore, all of the existing solutions can be said to require these large contact pads on the top, or upward facing surface of the substrate.
Therefore, a need existed to provide a device and method to overcome the above problems.